This invention is directed to air conditioning and refrigeration compressor control and more particularly, to control of multiple variable speed compressors.
Variable speed control of a compressor in a refrigeration or air conditioning application is often accomplished using a variable speed drive. This allows the removal of all unloading hardware from the compressor system. In typical applications involving more than one compressor, such as multiple circuit chillers, multiplexed compressor chillers, refrigeration, compressor racks, a variable speed control could be used with each compressor to selectively unload compressors as necessary based on system demand. Variable speed drives are expensive and therefore, multiple compressor systems requiring multiple variable speed drives also become extensively more expensive. In addition, the need for multiple variable speed drives adds to the complexity and size of the air conditioning or refrigeration system.
There exists a need therefore, for a solution which allows for the reduction in the number of variable speed drives required for multi-compressor systems so as to reduce cost and system complexity.
An object of this invention is to provide a multiple compressor system having a single variable speed drive for unloading compressors, which provides the capability to match cooling capacity with system load
Another object of this invention is to provide a lower cost, less complex variable speed compressor systems with multiple compressors and motors, having a single variable speed drive.
In accordance with foregoing objects and following advantages, A system for variable speed control of a plurality of compressors under variable load demand is provided. The system includes a constant power source and a plurality of compressor motors having switches to connect with the constant power source. The system further includes a variable speed drive for driving each of the plurality of compressor motors at variable speed, wherein each of the plurality of compressor motors includes a switch to connect with the variable speed drive. Each of the plurality of compressor motors is selectively electrically connected with the variable speed drive and the constant power source via the switches, for driving the each of the plurality of motors at either variable or constant speed in response to compressor load demands.